1. Field of the Invention
This invention relates generally to electrical delay lines, and more particularly relates to an ultraminiature low loss coaxial delay line for time delaying electrical signals using miniature coaxial cable, amplifiers and switching elements.
2. Description of the Prior Art
Many electronic systems require a controllable time delay element in order to properly process and analyze the electronic signals generated by the system. Typically, time delay of an electronic signal is accomplished by introducing the signal to a coaxial transmission line having a known dielectric, impedance and length. The time delay in seconds of an electronic signal associated with a particular coaxial transmission line is determined by the expression: ##EQU1## where e.sub.r =dielectric constant of the coaxial transmission line relative to air
L=length of coaxial transmission line in meters PA1 C=speed of light in free space in meters/seconds PA1 f=electronic signal frequency in MHz PA1 e.sub.r =dielectric constant relative to air PA1 F.sub.p =power factor of the dielectric at a frequency F
One of the drawbacks to utilizing a coaxial transmission line as a delay line is the resulting electronic signal attenuation. Typically, in order to reduce the amount of electronic signal attenuation produced by a coaxial delay line, delay lines are produced with coaxial transmission lines having relatively large outer diameters. It is well known that signal attenuation can be significantly reduced in this manner because signal attenuation is inversely related to the outer diameter of the coaxial transmission line given a fixed line impedance. Typically, coaxial transmission lines have outer diameters of 0.050 inches to 0.25 inches.
It is also known that the amount of attenuation occurring per 100 feet of coaxial transmission line is given by: ##EQU2## where ##EQU3## D=diameter of the inner surface of the outer coaxial conductor in inches d=diameter of the center conductor in inches
In light of the above and in order to reduce the amount of signal attenuation, large and heavy coaxial transmission delay lines are traditionally used to obtain a desired electronic signal delay without producing significant unwanted signal attenuation. However, while producing the required time delay without significant signal loss, these traditional delay lines are among the largest and heaviest components of many electronic systems. These bulky and heavy delay lines account for a significant percentage of the size and weight of an electrical system. For example, in order to produce a relatively short 49.7 nsec signal delay with a traditional coaxial delay line, approximately 34.5 feet of RG 142 coaxial transmission cable weighing approximately 1.6 pounds is required.